The present invention realtes to the physical packaging of electronics components, and more particularly relates to improved apparatus for cooling multiple cages or bays of components.
Many electronics systems use a packaging approach involving cages or bays which hold a number of individual cards, books, or other units of components, where the individual units are electrically connected to each other by means of a backplane bus. Data-processing systems, for example, commonly use this type of packaging.
The increasing density of electronics circuits and their increasing speed of operation both demand physically smaller packages. On the other hand, their power dissipation has not scaled down to quite the same extent, so that heat dissipation limits the extent to which the packaging size can be decreased. Sophisticated techniques have been developed for cooling miniaturized equipment, but these techniques also tend to be expensive and complicated.
One packaging approach which has many electrical and structural advantages places two cages of cards or books in an enclosure back to back on both sides of a backplane bus, so that the books plug into parallel sockets on both sides of the backplane. This decreases the electrical length of the bus, allowing faster operation. It provides a structurally compact unit, having a high ratio of usable volume to surface area. This approach, however, creates cooling problems. The conventional method, drawing air in a straight line from the top of the cage and through the books and the bottom of the cage into a fan and thence to an exhaust port, requires large spaces at the top and bottom of the cage for air inlet and exhaust. Designs without relatively large plenums typically experience high pressure losses (high impedance), poor airflow distribution (hot spots), and high air velocity (higher noise levels). The double-sided backplane cannot feasibly be made mechanically porous enough to allow air flow though one set of books, the backplane, then the second set of books in a straight line.